The present invention relates to a semiconductor electric motor and, more particularly, to a semiconductor electric motor having a novel structure that employs a rotary transformer to excite a rotor that serves as a field magnet, for obtaining position-sensing signals.
Servomotors and other electric motors used in industrial equipments are required to be small, powerful, have a long life and low inertia, and generate low noise. A cylindrical semiconductor electric motor may satisfy these requirements. However, this motor has several disadvantages as follows.
First, Hall effect devices are utilized as elements for sensing positions. This severely limits temperature increase, and hence a small-sized motor of this kind cannot produce a large output.
Secondly, the rotor serving as the field magnet is made of a ferrite magnet. Therefore, the magnet field is not strong. Where a large output is needed, a motor that is fabricated in large size must be provided. Thus, the output increase is limited. Accordingly, where a small-sized, semiconductor motor that produces a large output is necessitated, an expensive sintered magnet using a rare metal must be employed.
Thirdly, if position-sensing devices other than Hall effect devices are used, the motor has a special structure which is not adapted to be mass-produced. Hence, it is expensive to manufacture.